Ultrasonography

 Ultrasonography (USG) is application of
medical with ultrasound-based imaging
diagnostic technique used to visualize internal
organs, their size, structure and their
pathological lesions.

 Ultrasonography is widely utilized in medicine,
primarily in gastroenterology, cardiology,
gynecology and obstetrics, urology and
endocrinology. It is possible to perform
diagnosis or therapeutic procedures with the
guidance of ultrasonography (for instance
biopsies or drainage of fluid collections).

 In physics, the term "ultrasound" applies
to all acoustic energy (longitudinal,
mechanical wave) with a frequency
above the audible range of human
hearing. The audible range of sound is 20
hertz-20 kilohertz. Ultrasound is frequency
greater than 20 kilohertz.

Strengths of ultrasound imaging:
 It images muscle and soft tissue very well and is particularly useful for
delineating the interfaces between solid and fluid-filled spaces.
 It renders "live" images, where the operator can dynamically select the most
useful section for diagnosing and documenting changes, often enabling
rapid diagnoses.
 It shows the structure as well as some aspects of the function of organs.
 It has no known long-term side effects and rarely causes any discomfort to
the patient.
 Equipment is widely available and comparatively flexible; examinations can
be performed at the bedside.

Weaknesses of ultrasound imaging:
 Ultrasound cannot penetrate bone and performs poorly when there is air
between the scanner and the organ of interest. For example, overlying gas in
the gastrointestinal tract often makes ultrasound scanning of the pancreas
difficult.
 Even in the absence of bone or air, the depth penetration of ultrasound is
limited, making it difficult to image structures that are far removed from the
body surface, especially in obese patients.
 The method is operator-dependent. A high level of skill and experience is
needed to acquire good-quality images and make accurate diagnoses.

 Ultrasonography is generally considered a "safe" imaging modality. However slight
detrimental effects have been occasionally observed (see below). Diagnostic
ultrasound studies of the fetus are generally considered to be safe during
pregnancy. This diagnostic procedure should be performed only when there is a
valid medical indication, and the lowest possible ultrasonic exposure setting
should be used to gain the necessary diagnostic information under the "as low as
reasonably achievable" or ALARA principle.

 World Health Organizations technical report series 875(1998).supports that
ultrasound is harmless: "Diagnostic ultrasound is recognized as a safe, effective,
and highly flexible imaging modality capable of providing clinically relevant
information about most parts of the body in a rapid and cost-effective fashion".
Although there is no evidence ultrasound could be harmful for the fetus, US Food
and Drug Administration views promotion, selling, or leasing of ultrasound
equipment for making "keepsake fetal videos" to be an unapproved use of a
medical device.

 Studies on the safety of ultrasound
A study at the Yale School of Medicine found a correlation between prolonged
and frequent use of ultrasound and abnormal neuronal migration in mice. A
meta-analysis of several ultrasonography studies found no statistically significant
harmful effects from ultrasonography, but mentioned that there was a lack of
data on long-term substantive outcomes such as neurodevelopment.

Ultrasound information can be displayed in several ways.
 A-mode: This display mode is the simplest; signals are recorded
as spikes on a graph. The vertical (Y) axis of the display shows the
echo amplitude, and the horizontal (X) axis shows depth or
distance into the patient. This type of ultrasonography is used for
ophthalmologic scanning.
 B-mode (gray-scale): This mode is most often used in diagnostic
imaging; signals are displayed as a 2-dimensional anatomic
image. B-mode is commonly used to evaluate the developing
fetus and to evaluate organs, including the liver, spleen, kidneys,
thyroid gland, testes, breasts, and prostate gland. B-mode
ultrasonography is fast enough to show real-time motion, such as
the motion of the beating heart or pulsating blood vessels. Real-
time imaging provides anatomic and functional information.
 M-mode: This mode is used to image moving structures; signals
reflected by the moving structures are converted into waves
that are displayed continuously across a vertical axis. M-mode is
used primarily for assessment of fetal heartbeat and in cardiac
imaging, most notably to evaluate valvular disorders.

 Doppler: This type of ultrasonography is used to assess blood flow.
Doppler ultrasonography uses the Doppler effect (alteration of
sound frequency by reflection off a moving object). The moving
objects are RBCs in blood. Direction and velocity of blood flow can
be determined by analyzing changes in the frequency of sound
waves:
› If a reflected sound wave is lower in frequency than the
transmitted sound wave, blood flow is away from the transducer.
› If a reflected sound wave is higher in frequency than the
transmitted sound wave, blood flow is toward the transducer.
› The magnitude of the change in frequency is proportional to
blood flow velocity.
› Changes in frequency of the reflected sound waves are
converted into images showing blood flow direction and
velocity.

For color Doppler ultrasonography, color is superimposed on a gray-
scale anatomic image. The color indicates direction of blood flow.
By convention, red indicates flow toward and blue indicates flow
away from the transducer.

Doppler ultrasonography is also used to evaluate vascularity of
tumors and organs, to evaluate heart function (e.g., as for
echocardiography), to detect occlusion and stenosis of blood
vessels, and to detect blood clots in blood vessels (e.g., in deep
venous thrombosis).

System Description
Anesthesiology Ultrasound is commonly used by anesthesiologists (Anesthetists)
to guide injecting needles when placing local anesthetics
solutions near nerves
Cardiology Echocardiography is an essential tool in cardiology, to
diagnose e.g. dilatation of parts of the heart and function of
heart ventricles and valves
Emergency Point of care ultrasound has many applications in the
Medicine Emergency Department, including the Focused Assessment
with Sonography for Trauma (FAST) exam for assessing
significant hemoperitoneum or pericardial tamponade after
trauma. Ultrasound is routinely used in the Emergency
Department to expedite the care of patients with right upper
quadrant abdominal pain who may have gallstones or
cholecystitis.
Gastroenterology In abdominal sonography, the solid organs of the abdomen
such as the pancreas, aorta, inferior vena cava, liver, gall
bladder, bile ducts, kidneys, and spleen are imaged. Sound
waves are blocked by gas in the bowel and attenuated in
different degree by fat, therefore there are limited diagnostic
capabilities in this area. The appendix can sometimes be seen
when inflamed e.g. appendicitis.

Neonatology for basic assessment of intra-cerebral structural abnormalities, bleeds,
ventricular mealy or hydrocephalus and anoxic insults (Per ventricular
leukemic laical). The ultrasound can be performed through the soft spots
in the skull of a newborn infant (Fontanels) until these completely close at
about 1 year of age and form a virtually impenetrable acoustic barrier
for the ultrasound. The most common site for cranial ultrasound is the
anterior fontanels. The smaller the fontanels, the poorer the quality of the
picture
Neurology for assessing blood flow and stenos in the carotid arteries (Carotid
ultrasonography) and the big intra cerebral arteries
Urology to determine, for example, the amount of fluid retained in a patient's
bladder. In a pelvic sonogram, organs of the pelvic region are imaged.
This includes the uterus and ovaries or urinary bladder. Men are
sometimes given a pelvic sonogram to check on the health of their
bladder and prostate. There are two methods of performing a pelvic
sonography - externally or internally. The internal pelvic sonogram is
performed either trans vaginally(in a woman) or trans rectally (in a man).
Sonographic imaging of the pelvic floor can produce important
diagnostic information regarding the precise relationship of abnormal
structures with other pelvic organs and it represents a useful hint to treat
patients with symptoms related to pelvic prolapsed, double
incontinence and obstructed defecation
Musculoskeletal tendons, muscles, nerves, ligaments, soft tissue masses, and bone
surfaces
Cardiovascular To assess patency and possible obstruction of arteries Arterial
sonography diagnose DVT (Thrombosonography) and determine extent
and severity of venous insufficiency (venosonography)
Obstetrics Obstetrical sonography is commonly used during pregnancy to check on
the development of the fetus

Using a conventional diagnostic ultrasound
device and a position sensing device the
possibility of creating three dimensional
ultrasound images has been established.
The 2-D ultrasound images of a Simens
Sonoline SI400 are fit together with a Silicon
Graphics Workstation to build a 3-D volume
dataset. The position, where the grayscale
data are inserted in the virtual volume is
dependent on the location of the
ultrasound head at the moment of
ultrasound recording.

An ultrasound head of a medical imaging
ultrasound device is connected to a sensor
of the position sensing system Optotrac
from Northern Digital. The location and
orientation of the sound head can then be
measured by the Optotrac. The image
data of the Ultrasound device are
digitalized by a video card of a computer
and are provided to the software together
with the position information of the
ultrasound sensor. In the following figure the
arrangement is shown.

 Performance
The ultrasound head is moved slowly
across the body. The location and the
ultrasound image are recorded
continuously. Afterwards, the volume
data set, resulted from the compound of
ultrasound images, can be looked at by
volume visualization techniques.

 Results
The following images show volume
recordings of the abdominal area of a
human body.

Diagnostic sonography (ultrasonography) is
an ultrasound-based diagnostic imaging
technique used for visualizing subcutaneous
body structures including tendons, muscles,
joints, vessels and internal organs for
possible pathology or lesions different with
obstetric sonography is commonly used
during pregnancy and is widely recognized
by the public.

 Typical diagnostic sonographic scanners operate in the
frequency range of 1 to 18 megahertz, though
frequencies up to 50-100 megahertz has been used
experimentally in a technique known as bio microscopy
in special regions, such as the anterior chamber of eye.
The above frequencies are hundreds of times greater
than the limit of human hearing, which is typically
accepted as 20 kilohertz. The choice of frequency is a
trade-off between spatial resolution of the image and
imaging depth: lower frequencies produce less
resolution but image deeper into the body.

 Sonography (ultrasonography) is widely used in
medicine. It is possible to perform both diagnosis and
therapeutic procedures, using ultrasound to guide
interventional procedures (for instance biopsies or
drainage of fluid collections). Sonographers are medical Orthogonal planes
professionals who perform scans for diagnostic
purposes. Sonographers typically use a hand-held
of a 3 dimensional
probe (called a transducer) that is placed directly on sonographic
and moved over the patient. volume with
transverse and
 Sonography is effective for imaging soft tissues of the coronal
body. Superficial structures such as muscles, tendons,
testes, breast and the neonatal brain are imaged at a
measurements for
higher frequency (7-18 MHz), which provides better axial estimating fetal
and lateral resolution. Deeper structures such as liver cranial volume
and kidney are imaged at a lower frequency 1-6 MHz
with lower axial and lateral resolution but greater
penetration.

Therapeutic applications use ultrasound to bring heat or agitation into the
body. Therefore much higher energies are used than in diagnostic
ultrasound. In many cases the range of frequencies used are also very
different.
› Ultrasound is sometimes used to clean teeth in dental hygiene.
› Ultrasound sources may be used to generate regional heating and
mechanical changes in biological tissue, e.g. in occupational therapy,
physical therapy and cancer treatment. However the use of ultrasound in
the treatment of musculoskeletal conditions has fallen out of favor.
› Focused ultrasound may be used to generate highly localized heating to
treat cysts and tumors (benign or malignant), This is known as Focused
Ultrasound Surgery (FUS) or High Intensity Focused Ultrasound (HIFU).
These procedures generally use lower frequencies than medical
diagnostic ultrasound (from 250 kHz to 2000 kHz), but significantly higher
energies. HIFU treatment is often guided by MRI.
› Focused ultrasound may be used to break up kidney stones by lithotripsy.
› Ultrasound may be used for cataract treatment by phaco emulsification.
› Additional physiological effects of low-intensity ultrasound have recently
been discovered, e.g. its ability to stimulate bone-growth and its
potential to disrupt the blood-brain barrier for drug delivery.
› Pro-coagulant at 5-12 MHz,

Obstetric sonography
(ultrasonography) is the
application of medical
ultrasonography to obstetrics, in
which sonography is used to
visualize the embryo or fetus in
its mother's uterus (womb). The
procedure is often a standard Obstetric sonogram of a baby at
part of prenatal care, as it yields 16 weeks. The bright white circle
center-right is the head, which
a variety of information faces to the left. Features include
regarding the health of the the forehead at 10 o'clock, the left
mother and of the fetus, as well ear toward the center at 7 o'clock
and the right hand covering the
as regarding the progress of the eyes at 9:00.
pregnancy.

 Early pregnancy
The gestational sac can sometimes be visualized as early as four and a half weeks of gestation
(approximately two and a half weeks after ovulation) and the yolk sac at about five weeks
gestation. The embryo can be observed and measured by about five and a half weeks. The
heartbeat may be seen as early as 6 weeks, and is usually visible by 7 weeks gestation.
 Dating and growth monitoring
Gestational age is usually determined by the date of the woman's last menstrual period, and
assuming ovulation occurred on day fourteen of the menstrual cycle. Sometimes a woman
may be uncertain of the date of her last menstrual period, or there may be reason to suspect
ovulation occurred significantly earlier or later than the fourteenth day of her cycle. Ultrasound
scans offer an alternative method of estimating gestational age. The most accurate
measurement for dating is the crown-rump length of the fetus, which can be done between 7
and 13 weeks of gestation. After 13 weeks gestation, the fetal age may be estimated by the
bi-parietal diameter (the transverse diameter of the head), the head circumference, the
length of the femur (the longest bone in the body), and the many more fetal parameters that
have been measured and correlated with age over the last 30 years. Dating is more accurate
when done earlier in the pregnancy; if a later scan gives a different estimate of gestational
age, the estimated age is not normally changed but rather it is assumed the fetus is not
growing at the expected rate. Not useful for dating, the abdominal circumference of the fetus
may also be measured. This gives an estimate of the weight and size of the fetus and is
important when doing serial ultrasounds to monitor fetal growth.
 Fetal sex determination
Sonogram of male baby, with scrotum and penis in center of image
The sex of the baby can usually be determined by ultrasound at any time after 16 weeks, often
at the dating scan around 20 weeks into the pregnancy depending upon the quality of the
sonographic machine and skill of the operator. This is also the best time to have an ultrasound
done as most infants are the same size at this stage of development. Depending on the skill of
the sonographer, ultrasound may suffer from a high rate of false negatives and false positives.
This means care has to be taken in interpreting the accuracy of the scan.

 Ultrasonography of cervix
Obstetric sonography has become useful in the assessment of the cervix in
women at risk for premature birth. A short cervix preterm is undesirable: At 24
weeks gestation a cervix length of less than 25 mm defines a risk group for
preterm birth, further, the shorter the cervix the greater the risk.[ It also has
been helpful to use ultrasonography in women with preterm contractions, as
those whose cervix length exceed 30 mm are unlikely to deliver within the
next week.

 Abnormality screening
In some countries, routine pregnancy sonographic scans are performed to
detect developmental defects before birth. This includes checking the status
of the limbs and vital organs, as well as (sometimes) specific tests for
abnormalities. Some abnormalities detected by ultrasound can be
addressed by medical treatment in uterus or by prenatal care, though
indications of other abnormalities can lead to a decision regarding abortion.

Perhaps the most common such test uses a measurement of the nuchal
translucency thickness ("NT-test", or "Nuchal Scan"). Although 91% of fetuses
affected by Down syndrome exhibit this defect, 5% of fetuses flagged by the
test do not have Down syndrome.

Ultrasound may also detect fetal organ anomaly. Usually scans for this type
of detection are done around 18 to 20 weeks of gestational age.

Sonogram of male baby,
with scrotum and penis in Baby at 14 weeks
center of image

 From sound to image
The creation of an image from sound is done in three steps
- producing a sound wave, receiving echoes, and
interpreting those echoes.

 In ultrasonography, a signal generator is combined with a
transducer. Piezoelectric crystals in the signal generator
convert electricity into high-frequency sound waves,
which are sent into tissues. The tissues scatter, reflect, and
absorb the sound waves to various degrees. The sound
waves that are reflected back (echoes) are converted
into electric signals. A computer analyzes the signals and
displays the information on a screen.

 Ultrasonography is portable, widely available, and safe.
No radiation is used.

 A sound wave is typically produced by a piezoelectric transducer encased in a housing
which can take a number of forms. Strong, short electrical pulses from the ultrasound
machine make the transducer ring at the desired frequency. The frequencies can be
anywhere between 2 and 18 MHz The sound is focused either by the shape of the
transducer, a lens in front of the transducer, or a complex set of control pulses from the
ultrasound scanner machine (Beam forming). This focusing produces an arc-shaped
sound wave from the face of the transducer. The wave travels into the body and comes
into focus at a desired depth.

 Older technology transducers focus their beam with physical lenses. Newer technology
transducers use phased array techniques to enable the sonographic machine to
change the direction and depth of focus. Almost all piezoelectric transducers are made
of ceramic.

 Materials on the face of the transducer enable the sound to be transmitted efficiently
into the body (usually seeming to be a rubbery coating, a form of impedance
matching). In addition, a water-based gel is placed between the patient's skin and the
probe.

 The sound wave is partially reflected from the layers between different tissues.
Specifically, sound is reflected anywhere there are density changes in the body: e.g.
blood cells in blood plasma, small structures in organs, etc. Some of the reflections return
to the transducer.

The return of the sound wave to the
transducer results in the same process
that it took to send the sound wave,
except in reverse. The return sound wave
vibrates the transducer, the transducer
turns the vibrations into electrical pulses
that travel to the ultrasonic scanner
where they are processed and
transformed into a digital image.

 The sonographic scanner must determine three things from each received
echo:
› How long it took the echo to be received from when the sound was
transmitted.
› From this the focal length for the phased array is deduced, enabling a
sharp image of that echo at that depth (this is not possible while
producing a sound wave).
› How strong the echo was. It could be noted that sound wave is not a click,
but a pulse with a specific carrier frequency. Moving objects change this
frequency on reflection, so that it is only a matter of electronics to have
simultaneous Doppler sonography
 Once the ultrasonic scanner determines these three things, it can locate which
pixel in the image to light up and to what intensity and at what hue if
frequency is processed (see red shift for a natural mapping to hue).
 Transforming the received signal into a digital image may be explained by
using a blank spreadsheet as an analogy. First picture a long, flat transducer at
the top of the sheet. Send pulses down the 'columns' of the spreadsheet (A, B,
C, etc.). Listen at each column for any return echoes. When an echo is heard,
note how long it took for the echo to return. The longer the wait, the deeper
the row (1,2,3, etc.). The strength of the echo determines the brightness setting
for that cell (white for a strong echo, black for a weak echo, and varying
shades of grey for everything in between.) When all the echoes are recorded
on the sheet, we have a grayscale image.

Images from the sonographic scanner
can be displayed, captured, and
broadcast through a computer using a
frame grabber to capture and digitize
the analog video signal. The captured
signal can then be post-processed on
the computer itself

Ultrasonography

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